General Information

The player may request absolution from Oswald of Carim inside the belltower of the Undead Parish, after ringing the Bell of Awakening. The general purpose of this is to reset NPC hostility and allow the player to rejoin covenants they may have angered. This is achieved by removing the Sin obtained for committing those transgressions. Most NPCs become hostile when the player removes over 10% of their HP, and will remain permanently hostile toward the player until absolution is paid for.

Cost

The cost to absolve sin(s) is 500 souls per Soul Level, and it is not affected by the amount of times the player has sinned. A level 10 player will have to pay 5,000 souls, while a level 100 player will have to pay 50,000.

What absolution can do

Revert all hostile NPCs to normal, with one specific exception. See below.

Allow Covenants to be rejoined if the covenant leader was angered, but not killed.

Remove the Sin of killing Gwynevere. Oswald will allow you to pay for absolution after killing Gwynevere, and may tell you shortly after that you do not have sin. But the sin of killing Gwynevere is actually permanent, and it will eventually be placed upon your character again automatically.

Prevent Darkmoon invaders from invading you. Receiving indictment sin opens the player to Darkmoon invaders who are using the Blue Eye Orb, which Oswald cannot absolve. Killing Gwynevere opens the player to Darkmoon invaders who are using the Darkmoon Blade Covenant Ring, which Oswald also cannot absolve.

Revert either of the primordial serpents. The only way to get Darkstalker Kaathe or Frampt back is to start a new playthrough.

Notes

Oswald allows players to pay for absolution after destroying Gwynevere's illusion, and will inform them that they "have not sinned" if they attempt to pay again right after. This may give players a false sense of safety, thinking they have removed that sin. However, the sin of destroying Gwynevere's illusion is permanent, and automatically refreshes to be placed upon the player again when they revisit darkened Anor Londo. This means that absolution cannot prevent Darkmoon invasions in dark Anor Londo, and paying for it in this scenario is a waste of souls with no beneficial effect.

Paying for absolution after killing any NPC, where their services are no longer available, is also a waste of souls. There is no negative effect resulting from carrying the sin of killed NPCs (consult the sin page for more information). Absolution is only beneficial for de-aggroing living NPCs and unwelcoming covenants.